Bot Stract is used as its intended name was given - fuel.
Fuel is burned up during use -- the (small) function of *.993 determines how much fuel you burn in relation to how much the fuel is fueling your bot.
Each 500 Bot Stract gives 1 hp, capped at 4,500 bonus (which is a very large bonus -- an Elektra head only gives 1205 HP), which is 2,250,000 bot stract. In addition to this, the *.993 function is capped at 2,250,000, making the maximum fuel loss only equal to the bonus cap (4,500 bonus is equal to 15,750 bot stract consumed). Therefore, 15,750 bot stract is the most that can be consumed in one game. If you have 2,250,000+ bot stract, 15,750 is not much to forfeit for a major 4,500 HP bonus.
Check this thread for more info:
http://boutcheetah.zylongaming.com/index.php/topic,21431.0.html